1. Field of the Invention
The present invention relates to a process signal collecting apparatus. More specifically, the present invention relates to a novel process signal collecting apparatus for collecting two-value signals obtainable from two-value optical switches such as switches, setting means and the like provided for the purpose of process control in a plant such as of rolling mills in steel manufacture.
2. Description of the Prior Art
A process control system is employed in various plants such as a steel manufacturing plant for the purpose of process control of rolling mills. As is well known, a process control is adapted to control an operation of a plant system such as rolling mills in accordance with a sequential process as a function of the data of various data sources such as an open/close state of contents of various switches, setting means and the like. To that end, a process control system comprises a process signal collecting apparatus for determining a two-value state or a binary state of various devices, such as an open/close state of each contact of various switches, setting means and the like.
FIGS. 1 and 2 are block diagrams of conventional process signal collecting apparatuses. First referring to FIG. 1, an outline of a conventional process signal collecting apparatus will be described. The process signal collecting apparatus shown comprises a central processing unit 1, an input controller 2, and a level converting circuit 3. A plurality of contacts 41 to 4n are connected to the level converting circuit 3. These contacts 41 to 4n may comprise switches or setting means provided in rolling mills in a steel manufacturing plant. The level converting circuit 3 is adapted to convert relatively high control voltages being applied to the contacts 41 to 4n to a voltage level as low as 5 V which is suited for processing by the central processing unit 1. The two-value signals such as on/off signals of the respective switches 41 to 4n, as level converted by the level converting circuit 3, are applied to the input controller 2. The central processing unit 1 is adapted to supply an access signal for collecting the on/off signals to the input controller 2 and is also adapted to perform other processing. The input controller 2 is responsive to the access signal from the central processing unit 1 to provide the respective on/off signals from the contacts 41 to 4n in succession to the central processing unit 1. The central processing unit 1 is responsive to the on/off signals obtained from the contacts 41 to 4n to execute an operation for further process control.
Considering the case of rolling mills, for example, the apparatus could extend as long as 1 km and a rolling mill of such length comprises several hundred switches, setting means and the like distributed throughout the length. On the other hand, a process signal collecting apparatus is usually installed at a location spaced apart remotely from such rolling mills and connection of these several hundreds of switches and setting means to the above described level converting circuit 3 necessitates cables 5 of an increased length. Accordingly, the cost of installation of such cables is considerably increased. Since a number of cables 5 are coupled to the level converting circuit 3 in a concentrated manner, additional installation of new switches for connection of cables to the level converting circuit 3 makes such connection work extremely difficult.
Accordingly, an approach is considered in which several hundred switches are divided into a plurality of groups so that a local station may be provided in each of the groups, whereby switches as grouped are connected to each local station and the on/off signals collected by each local station are transmitted to the central processing unit 1 through a signal transmission cable. Such data collecting apparatus is shown in FIG. 2. Referring to FIG. 2, a plurality of local stations 6 are provided. Each local station 6 comprises a transmission control circuit 61, an input controller 62, and a level converting circuit 63. The level converting circuit 63 is connected to contacts 401 to 40n of a plurality of switches, setting means or the like, as grouped. The level converting circuit 63 is adapted to convert the levels of the on/off signals obtained from the contacts 401 to 40n. The input controller 62 receives in succession the on/off signals as level converted by the level converting circuit 63 and provides the same to the transmission control circuit 61. The transmission control circuit 61 serves to transmit the on/off signals in succession on a transmission cable 10.
The central processing unit 1 is coupled to an input controller 2, a buffer memory 7, an output controller 8, and a transmission control circuit 9. The buffer memory 7 comprises storing regions for storing the respective on/off signals of the contacts 401 to 40n connected to each of the local stations 6. The transmission cable 10 is connected to the transmission control circuit 9. The transmission control circuit 9 receives in succession the on/off signals obtained from the local stations 6 and provides the same to the output controller 8. The output controller 8 is responsive to the on/off signals, thereby to designate in succession the addresses of the buffer memory 7. When the buffer memory 7 is addressed, the respective on/off signals are stored in the corresponding storing regions of the contacts 401 to 40n. The central processing unit 1 is loaded in succession with the on/off signals obtained from the buffer memory 7 through the input controller 2. Thus the on/off signals from the respective local stations 6 are stared in succession in the buffer memory. The central processing unit 1 performs further process control based on the on/off signals obtained from the respective contacts 401 to 40n as stored in the buffer memory 7.
By disposing a plurality of local stations 6 distributed in conjunction with rolling mills, for example, it is possible to shorten the distances between the respective contacts 401 to 40n and the local stations 6. In addition, since a number of cables are connected to the respective local stations 6 in a scattered manner, any work required for addition of new switches can be achieved with relative simplicity.
Meanwhile, the above described local stations 6 each have a predetermined number of contacts which are connectable and hence it is largest efficient to connect the largest possible number of contacts within such predetermined number. Therefore, if and when the number of contacts being connected to a given local station exceeds the number of lines connectable to the local station, those contacts of the excessive number of contacts need be connected to another local station having a spare number of connections, which necessitates a complicated consideration of the local stations with those number of contacts. Since those excessive number of contacts are usually connected to a local station less remotely located, this accordingly necessitates an elongated length of cables connected to these contacts. Accordingly, when the respective contacts are connected to the local stations 6, both the number of contacts being connectable to the respective local stations 6 and the length of each cable need be taken into consideration in determining connection, which necessitates excessive labor and time in designing the whole system.
In addition, a number of noise sources such as motors, electromagnetic valves and the like are usually provided in the vicinity of rolling mills, which are liable to generate continuously electric surges. If and when such electric surges are transferred on the transmission cable 10, it is liable that erroneous on/off signals are stored in the buffer memory 7, which could be a cause of malfunction of the central processing unit 1 in a process control.